Pneumatic jacks are known for a large number of uses. Most of these jacks have a jack body and a shaft displaceable longitudinally relative to the jack body. This type of arrangement permits obtaining jacks adapted to occupy for example three working positions, one corresponding to the maximum extension of said shaft, the other corresponding to the minimum extension of said shaft and the third corresponding to an intermediate extension. In this case, the jack body comprises two membranes delimiting three chambers and the shaft is secured to the central portion of each of the membranes, which complicates the production of the assembly and limits the number of positions adapted to be occupied.
The object of the present invention is to provide a jack whose number of working positions is unlimited and which is susceptible of being produced by means of a small number of simple and standard pieces.
Another object of the invention is to provide a modular jack comprising several chambers, one chamber corresponding to a module, said modules being adapted to be mounted in series, in parallel or permitting the production of a push-pull type actuator.